Mutation of residue Phe97 to Leu disrupts the central allosteric pathway in Scapharca dimeric hemoglobin

Residue Phe97, which is thought to play a central role in the cooperative functioning of Scapharca dimeric hemoglobin, has been mutated to leucine to test its proposed role in mediating cooperative oxygen binding. This results in an 8-fold increase in oxygen affinity and a marked decrease in cooperativity. Kinetic measurements of ligand binding to the Leu97 mutant suggest an altered unliganded (deoxy) state, which has been confirmed by high resolution crystal structures in the unliganded and carbon monoxide-liganded states. Analysis of the structures at allosteric end points reveals them to be remarkably similar to the corresponding wild-type structures, with differences confined to the disposition of residue 97 side chain, F-helix geometry, and the interface water structure. Increased oxygen affinity results from the absence of the Phe97 side chain, whose tight packing in the heme pocket of the deoxy state normally restricts the heme from assuming a high affinity conformation. The absence of the Phe97 side chain is also associated with diminished cooperativity, since Leu97 packs in the heme pocket in both states. Residual cooperativity appears to be coupled with observed structural transitions and suggests that parallel pathways for communication exist in Scapharca dimeric hemoglobin.     

Cerebral blood flow velocity in relation to cerebral blood flow, cerebral metabolic rate for oxygen, and electroencephalogram analysis during isoflurane anesthesia in dogs

The purpose of this study was to correlate changes in cerebral blood flow velocity (Vmean) with cerebral blood flow (CBF) during isoflurane anesthesia in dogs. The relation between cerebral oxygen consumption (CMRO2) and electroencephalogram (EEG) analysis also was investigated. Blood flow velocity was measured in the middle cerebral artery using a pulsed transcranial Doppler (TCD). CBF was measured with radioactive microspheres. EEG was measured over both hemispheres and median EEG frequency (median frequency) was calculated after fast Fourier transformation. Baseline anesthesia was maintained with 50% nitrous oxide in oxygen and 50 micrograms.kg-1 x h-1 fentanyl. Animals of Group I (control, n = 6) were not given isoflurane. Data were recorded at baseline, and at 30, 60, and 90 min. There was no significant change in any variable over time. In Group II (n = 7), data were recorded at baseline and at 1%, 2%, and 3% end-tidal isoflurane. Mean arterial pressure was maintained at baseline levels by phenylephrine infusion. CBF increased from 70.8 +/- 10.6 mL.100g-1 x min-1 at baseline to 146.1 +/- 36.9 mL.100 g-1 x min-1 with 3% isoflurane (P < 0.01). Vmean increased from 38.3 +/- 6.7 cm/s to 65.6 +/- 9.7 cm/s (P < 0.01). The correlation between relative changes in CBF and Vmean was r = 0.94 (P < 0.01). With 1% isoflurane the EEG shifted to slow-wave, high-voltage activity, and median frequency decreased from 5.9 +/- 0.7 Hz to 1.4 +/- 0.4 Hz (P < 0.05). Median frequency was not decreased further during 2% and 3% isoflurane anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immortalized connexin43 knockout cell lines display a subset of biological properties associated with the transformed phenotype

Immortalized cells from embryonic connexin43 knockout mice (Cx43-/-) and homozygous littermates (Cx43+/+) were cloned and characterized to determine whether the absence of Cx43 function would induce observable phenotypic changes. Cells of the Cx43+/+ clones expressed Cx43 and engaged in gap junctional communication with 10-12 neighboring cells. The Cx43-/- cells were devoid of Cx43 and communicated to less than 1 cell. Electrophysiological analysis indicated that the Cx43-/- cells communicated through Cx45 channels from 8-80-fold less than did the Cx43+/+ subclones, which seemed to communicate through Cx43 and Cx45 channels. The Cx43-/- clones grew at faster rates and to higher saturation densities, had a more spindly morphology, were more refractile, and adhered less well to the substratum than did the Cx43+/+ clones. Reintroducing the Cx43 gene into the Cx43-/- clones resulted in three subclones that communicated to 3-4 cells. Partial restoration of gap junctional communication in the three subclones was accompanied by reduced growth rates and saturation densities (2-fold compared to that of parental Cx43-/- clones) but no reversions in morphology or cell-substratum adhesion. The increased growth rates and saturation densities, altered morphology, and decreased cell adhesion displayed by the Cx43-/- clones reflect a subset of the properties of transformed cells. These studies advance the hypothesis that loss of Cx43 function during development may cause cells to acquire a preneoplastic condition.     

Effects of chorion type on variation in cord blood cholesterol of monozygotic twins

Cholesterol levels were measured in the cord blood of 30 pairs of monochorionic and 22 pairs of dichorionic monozygotic (MZ) twins. Cholesterol levels were found to be significantly higher in female twins when data was combined over chorion type. The type of chorionic development had no significant effect on variation among twin pairs. Chorion type did, however, have a significant effect on the within-pair variation. The variation within dichorionic pairs was more than five times that within monochorionic pairs (P less than .01). This result suggests that the variation in placentation has a significant effect on within-pair variation in serum cholesterol of newborn MZ twins.     

Calcium dependence and binding in cultures of Histoplasma capsulatum

Histoplasma capsulatum is a pathogenic fungus with two distinct morphologies and lifestyles. The saprophytic form of this organism, a mold, thrives in soil and is especially abundant in the Ohio and Mississippi River valleys. Its parasitic counterpart, a yeast, colonizes phagolysosomes of mammalian macrophages. We have observed a major difference in the calcium requirements of the two forms of Histoplasma, potentially implicating the phagolysosome as a calcium-limiting compartment. Deprivation of calcium by the addition of EGTA to culture media inhibited the growth of mycelial H. capsulatum but had no effect on yeast growth in vitro. In addition, yeasts released a calcium-binding protein (CBP) detectable by a 45CaCl2 blotting technique. CBP was a major component of yeast culture supernatant and was also detectable by ruthenium red staining, another assay for calcium-binding activity. Conversely, mycelial H. capsulatum did not produce CBP, a finding that correlates with the dependence of mycelia on calcium for growth. We also describe here the purification of CBP from yeast culture supernatant by reversed-phase high-pressure liquid chromatography.